Theoretical models for the production of relativistic jets from active galactic nuclei predict that jet power arises from the spin and mass of the central supermassive black hole, as well as from the ...magnetic field near the event horizon. The physical mechanism underlying the contribution from the magnetic field is the torque exerted on the rotating black hole by the field amplified by the accreting material. If the squared magnetic field is proportional to the accretion rate, then there will be a correlation between jet power and accretion luminosity. There is evidence for such a correlation, but inadequate knowledge of the accretion luminosity of the limited and inhomogeneous samples used prevented a firm conclusion. Here we report an analysis of archival observations of a sample of blazars (quasars whose jets point towards Earth) that overcomes previous limitations. We find a clear correlation between jet power, as measured through the γ-ray luminosity, and accretion luminosity, as measured by the broad emission lines, with the jet power dominating the disk luminosity, in agreement with numerical simulations. This implies that the magnetic field threading the black hole horizon reaches the maximum value sustainable by the accreting matter.
The jet–disc connection in AGN Sbarrato, T; Padovani, P; Ghisellini, G
Monthly notices of the Royal Astronomical Society,
11/2014, Letnik:
445, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present our latest results on the connection between accretion rate and relativistic jet power in active galactic nuclei (AGN), by using a large sample which includes mostly blazars, but contains ...also some radio galaxies. The jet power can be traced by γ-ray luminosity in the case of blazars, and radio luminosity for both classes. The accretion-disc luminosity is instead traced by the broad emission lines. Among blazars, we find a correlation between broad line emission and the γ-ray or radio luminosities, suggesting a direct tight connection between jet power and accretion rate. We confirm that the observational differences between blazar subclasses reflect differences in the accretion regime, but with blazars only we cannot properly access the low-accretion regime. By introducing radio galaxies, we succeed in observing the fingerprint of the transition between radiatively efficient and inefficient accretion discs in the jetted AGN family. The transition occurs at the standard critical value L
d/L
Edd ∼ 10−2 and it appears smooth. Below this value, the ionizing luminosity emitted by the accretion structure drops significantly.
We study the relation between the mass accretion rate, the jet power and the black hole mass of blazars. With this aim, we make use of the Sloan Digital Sky Survey and the 11-month catalogue of ...blazars detected at energies larger than 100 MeV by the Large Area Telescope onboard the Fermi satellite. This allows us to construct a relatively large sample of blazars with information about both the luminosity (or upper limits) of their emission lines (used as a proxy for the strength of the disc luminosity) and the luminosity of the high-energy emission (used as a proxy for the jet power). We find a good correlation between the luminosity of the broad lines and the γ-ray luminosities as detected by Fermi, both using the absolute values of the luminosities and normalizing them to the Eddington value. The data we have analysed confirm that the division of blazars into BL Lacertae objects (BL Lacs) and flat spectrum radio quasars (FSRQs) is controlled by the line luminosity in Eddington units. For small values of this ratio, the object is a BL Lac, while it is a FSRQ for large values. The transition appears to be smooth, but a much larger number of objects is needed to confirm this point.
High-energy observations of extreme BL Lac objects, such as 1ES 0229+200 or 1ES 0347−121, recently focused interest both for blazar and jet physics and for the implication on the extragalactic ...background light and intergalactic magnetic field estimate. However, the number of these extreme highly peaked BL Lac objects (EHBL) is still rather small. Aiming at increase their number, we selected a group of EHBL candidates starting from the BL Lac sample of Plotkin et al. (2011), considering those undetected (or only barely detected) by the Large Area Telescope onboard Fermi and characterized by a high X-ray versus radio flux ratio. We assembled the multiwavelength spectral energy distribution of the resulting nine sources, profiting of publicly available archival observations performed by Swift, GALEX, and Fermi satellites, confirming their nature. Through a simple one-zone synchrotron self-Compton model we estimate the expected very high energy flux, finding that in the majority of cases it is within the reach of present generation of Cherenkov arrays or of the forthcoming Cherenkov Telescope Array.
The first blazar observed at z > 6 Belladitta, S.; Moretti, A.; Caccianiga, A. ...
Astronomy and astrophysics (Berlin),
03/2020, Letnik:
635
Journal Article
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We present the discovery of PSO J030947.49+271757.31, the radio brightest (23.7 mJy at 1.4 GHz) active galactic nucleus (AGN) at
z
> 6.0. It was selected by cross-matching the NRAO VLA Sky Survey ...and the Panoramic Survey Telescope and Rapid Response System PS1 databases and its high-
z
nature was confirmed by a dedicated spectroscopic observation at the Large Binocular Telescope. A pointed
Neil Gehrels Swift
Observatory XRT observation allowed us to measure a flux of ∼3.4 × 10
−14
erg s
−1
cm
−2
in the 0.5–10 keV energy band, which also makes this object the X-ray brightest AGN ever observed at
z
> 6.0. Its flat radio spectrum (
α
νr
< 0.5), very high radio loudness (
R
> 10
3
), and strong X-ray emission, compared to the optical, support the hypothesis of the blazar nature of this source. Assuming that this is the only blazar at this redshift in the surveyed area of sky, we derive a space density of blazars at
z
∼ 6 and with
M
1450 Å
< −25.1 of 5.5
+11.2
−4.6
× 10
−3
Gpc
−3
. From this number, and assuming a reasonable value of the bulk velocity of the jet (Γ = 10), we can also infer a space density of the entire radio-loud AGN population at
z
∼ 6 with the same optical/UV absolute magnitude of 1.10
+2.53
−0.91
Gpc
−3
. Larger samples of blazars will be necessary to better constrain these estimates.
At redshift larger than 3 there is a disagreement between the number of blazars (whose jet is pointing at us) and the number of expected parents (whose jet is pointing elsewhere). Now we strengthen ...this claim because (i) the number of blazars identified within the Sloan Digital Sky Survey (SDSS)+Faint Images of the Radio Sky at Twenty-cm (FIRST) survey footprint increased, demanding a more numerous parent population, and (ii) the detected blazars have a radio flux large enough to be above the FIRST flux limit even if the jet is slightly misaligned. The foreseen number of these slightly misaligned jets, in principle detectable, is much larger than the radio-detected sources in the FIRST+SDSS survey (at redshift larger than 4). This argument is independent of the presence of an isotropic radio component, such as the hotspot or the radio lobe, and does not depend on the bulk Lorentz factor Γ. We propose a scenario that ascribes the lack of slightly misaligned sources to an overobscuration of the nucleus by a ‘bubble’ of dust, possibly typical of the first high-redshift quasars.
Jetted radio-quiet quasars at z > 5 Sbarrato, T.; Ghisellini, G.; Giovannini, G. ...
Astronomy and astrophysics (Berlin),
11/2021, Letnik:
655
Journal Article
Recenzirano
Odprti dostop
We report on the JVLA observations of three high-redshift active galactic nuclei (AGNs) that have black hole masses estimated to be among the largest known. Two of them, SDSS J0100+2802 and SDSS ...J0306+1853 at redshift 6.326 and 5.363, respectively, are radio-quiet AGNs according to the classic definition, while the third (B2 1023+25 at
z
= 5.284) is a powerful blazar. The JVLA data clearly show a radio structure in the first source and a radio emission with a relatively steep radio spectrum in the second one, indicating the presence of a radio jet and a diffuse component. Therefore, being radio-quiet does not exclude the presence of a powerful relativistic jet, which has important consequences on population studies and on the ratio between jetted and non-jetted AGNs. We can estimate the viewing angle of these jets, and this allows us to find, albeit with some uncertainty, the density of black holes with a mass in excess of 10
10
M
⊙
at high redshifts. We found that their density in jetted AGNs is very large in the redshift bin 5–6 and comparable with the overall AGN population of the same optical luminosity. Jets might thus play a crucial role in the fast formation and evolution of the most massive black holes in the early Universe. They are more common than what is expected from wide radio surveys with milliJansky flux sensitivity. Deeper JVLA or very-long-baseline interferometry observations are key to discovering a possible relativistic jet population hiding in plain sight at very high redshift. The discovery of powerful relativistic jets associated with the most massive black holes in the early Universe revives the question: is the jet instrumental for a rapid growth of the black hole or, instead, is the black hole mass the main driver for the jet formation?
QSFit: automatic analysis of optical AGN spectra Calderone, G; Nicastro, L; Ghisellini, G ...
Monthly notices of the Royal Astronomical Society,
12/2017, Letnik:
472, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Abstract
We present QSFit (Quasar Spectral Fitting package), a new software package to automatically perform the analysis of active galactic nuclei (AGNs) optical spectra. The software provides ...luminosity estimates for the AGN continuum, the Balmer continuum, both optical and ultraviolet iron blended complex, host galaxy and emission lines, as well as width, velocity offset and equivalent width of 20 emission lines. Improving on a number of previous studies on AGN spectral analysis, QSFit fits all the components simultaneously, using an AGN continuum model which extends over the entire available spectrum, and is thus a probe of the actual AGN continuum whose estimates are scarcely influenced by localized features (e.g. emission lines) in the spectrum. We used QSFit to analyse 71 251 optical spectra of Type 1 AGN at z < 2 (obtained by the Sloan Digital Sky Survey, SDSS) and to produce a publicly available catalogue of AGN spectral properties. Such catalogue
allowed us (for the first time) to estimate the AGN continuum slope and the Balmer continuum luminosity on a very large sample, and to show that there is no evident correlation between these quantities the redshift. All data in the catalogue, the plots with best-fitting model and residuals, and the idl code we used to perform the analysis, are available on a dedicated website. The whole fitting process is customizable for specific needs, and can be extended to analyse
spectra from other data sources. The ultimate purpose of QSFit is to allow astronomers to run standardized recipes to analyse the AGN data, in a simple, replicable and shareable way.
We collect data at all frequencies for the new sources classified as unknown active galactic nuclei (AGNs) in the latest Burst Alert Telescope all-sky hard X-ray catalog. Focusing on the 36 sources ...with measured redshift, we compute their spectral energy distribution (SED) from radio to
γ
-rays with the aim to classify these objects. We apply emission models that attempt to reproduce the obtained SEDs, including: (i) a standard thin accretion disk together with an obscuring torus and a X-ray corona; (ii) a two temperature thick advection-dominated flow; (iii) an obscured AGN model, accounting for absorption along the line of sight at kiloelectronvolt energies and in the optical band; and (iv) a phenomenological model to describe the jet emission in blazar-like objects. We integrate the models with the SWIRE template libraries to account for the emission of the host galaxy. For every source we found a good agreement between data and our model. Considering that the sources were selected in the hard X-ray band, which is rather unaffected by absorption, we expected and found a large fraction of absorbed radio-quiet AGNs (31 out of 36) and some additional rare radio-loud sources (5 out of 36), since the jet emission in hard X-rays is important for aligned jets owing to the boost produced by the beaming effect. With our work we can confirm the hypothesis that a number of galaxies, whose optical spectra lack AGN emission features, host an obscured active nucleus. The approach we used proved to be efficient in rapidly identifying objects, which commonly used methods were not able to classify.
The radio-loud quasar SDSS J013127.34–032100.1 at a redshift z = 5.18 is one of the most distant radio-loud objects. The radio to optical flux ratio (i.e. the radio-loudness) of the source is large, ...making it a promising blazar candidate. Its overall spectral energy distribution, completed by the X-ray flux and spectral slope derived through Target of Opportunity Swift/X-ray Telescope observations, is interpreted by a non-thermal jet plus an accretion disc and molecular torus model. We estimate that its black hole mass is (1.1 ± 0.2) × 1010 M⊙ for an accretion efficiency η = 0.08, scaling roughly linearly with η. Although there is a factor ≳2 of systematic uncertainty, this black hole mass is the largest found at these redshifts. We derive a viewing angle between 3 and 5 deg. This implies that there must be other (hundreds) sources with the same black hole mass of SDSS J013127.34–032100.1, but whose jets are pointing away from Earth. We discuss the problems posed by the existence of such large black hole masses at such redshifts, especially in jetted quasars. In fact, if they are associated with rapidly spinning black holes, the accretion efficiency is high, implying a slower pace of black hole growth with respect to radio-quiet quasars.
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